I have been working on a Modal Cosmological Argument (MCA) for some time now, and I'm convinced that the key premise - the possibility premise - is rationally acceptable. However, given recent attempts at proving that a maximally great being is possible (see my previous post), demonstrating the possibility of a necessary being ought to be even easier, assuming that such a proof is correct. Before I provide the possibility proof, here's another look at the MCA:
1. Contingent beings exist.
2. It is possible that the collection of all contingent beings (CCB) has an external cause.
3. If an external cause exists, that cause is a necessary being.
4. Hence, a necessary being possibly exists.
5. Whatever is possibly necessary is necessary.
6. Therefore, a necessary being exists.
Let's reformulate the three axioms listed earlier:
A1. If a property is a great-making property, its negation is not a great-making property.
A2. If a property A is a great-making property and the property B is a necessary condition for A, then B is a great-making property.
A3. Being a necessary being is a great-making property.
Following these axioms is the proof that a necessary being possibly exists:
P1. If it's not possible that a necessary being exists, then every being has the property of being contingent.
P2. If every being has the property of being contingent, then being contingent is a necessary condition.
P3. If being contingent is a necessary condition, then being contingent is a great-making property. (From A2)
P4. Being contingent is not a great-making property. (From A1 and A3)
P5. Therefore, it is possible that a necessary being exists.